Impact Analysis of MR-Laminated Composite Structures

Laminated composite structures are being used in many applications, including aerospace, automobiles, and civil engineering applications, due to their high stiffness to weight ratio. However, composite structures suffer from low ductility and sufficient flexibility to resist against dynamic, particularly impact loadings. Recently, a new generation of laminated composite structures has been developed in which some layers have been filled fully or partially with magnetorheological (MR) fluids; hereafter we call them MR-laminated structures. The present article investigates the effects of MR fluid layers on vibration characteristics and specifically on impact loadings of the laminated composite beams. Experimental works have been conducted to study the dynamic performance of the MR-laminated beams

Emerging Trends in Mechatronics

Mechatronics is a multidisciplinary branch of engineering combining mechanical, electrical and electronics, control and automation, and computer engineering fields. The main research task of mechatronics is design, control, and optimization of advanced devices, products, and hybrid systems utilizing the concepts found in all these fields. The purpose of this special issue is to help better understand how mechatronics will impact on the practice and research of developing advanced techniques to model, control, and optimize complex systems. The special issue presents recent advances in mechatronics and related technologies. The selected topics give an overview of the state of the art and present new research results and prospects for the future development of the interdisciplinary field of mechatronic systems

Characterization and Microstructure-based Modeling of Magnetorheological Elastomers

Multi-functional magnetorheological elastomers (MREs) with magnetic-controlled properties offer great potential for enabling new technologies in a diverse range of industry sectors, such as automotive, aerospace, civil, and biomedical applications. The main objective of this research dissertation is to develop analysis models for magneto-mechanical properties of smart MREs and to propose design optimization strategies to optimally design a novel sandwich beam-type MRE-based adaptive tuned vibration absorber. The dissertation comprises three major interrelated parts. In the first part, a quasi-static microstructure-based model has been proposed to investigate the magneto-elastic properties of MREs. The elastic response of the MREs at zero magnetic field is initially studied by comparing the results of three hyperelastic material models. Then, a microscale model is developed for predicting the quasi-static response of MREs under an external magnetic field. The model considers magnetic interaction between particles distributed in the carrier elastomeric matrix according to regular lattice models for isotropic MREs and according to chain-like structure for anisotropic MREs. Several lattice models are proposed, and performance of each lattice is compared with their counterparts. Detailed explanation is provided on the characteristics of the proposed lattices and on the resulting changes in the microstructure properties of the MREs. The simulation results for different lattice models are then compared with the experimental measurements for both isotropic and anisotropic MRE samples using an advanced rheometer equipped with a magnetorheological (MR) device. In the second part, the dynamic magneto-mechanical properties of MREs are investigated. For this purpose, a dynamic physic-based model considering the microstructure of MREs is developed to accurately predict the frequency- and field-dependent linear viscoelastic properties of the material. The proposed model considers a cubic particle network in which magnetic particles are located at the junctures and connected with elastic springs. Using Langevin dynamics, the governing equations of motion of particles are derived to evaluate the relaxation spectrum associated with particles’ motion in parallel and normal directions with respect to the applied magnetic field. A dipole magnetic saturation model is also implemented to derive the storage and loss moduli of the MREs in terms of frequency and magnetic flux density. The material parameters in the proposed dynamic microstructure-based model have been identified using experimental tests. For this purpose, oscillatory shear tests were performed using the magneto-rheometer in linear viscoelastic region under a wide range of excitation frequency varying from 2 Hz to 100 Hz in presence of various levels of applied magnetic fields ranging from 0.0 T to 1.0 T. The viscoelastic properties, namely storage and loss moduli of both isotropic and anisotropic MREs, were subsequently measured and compared with those obtained using the developed model to quantitatively evaluate its performance. The third part of the present dissertation aims to investigate the application of MREs in developing a novel sandwich beam-shaped MRE-based adaptive tuned vibration absorber (MRE-ATVA). An MRE-ATVA comprised of a light-weight sandwich beam treated with an MRE core layer and two electromagnets installed at both free ends is proposed. The MRE-ATVA is designed to have a lightweight and compact structure and the electromagnets provide the magnetic field required to activate the MRE layer while also act as the resonator of the absorber. The finite element (FE) model of the proposed MRE-ATVA and magnetic model of the electromagnets with three different potential designs are developed and combined to evaluate the frequency range of the absorber under varying magnetic field intensity. The results of the developed models are validated in multiple stages with available analytical and simulation data. The developed models are then utilized to formulate the multidisciplinary design optimization problem to maximize the operating frequency range of the MRE-ATVA while respecting constraints of weight, size, mechanical stress, and sandwich beam deflection. The optimization problem is solved combining the gradient based sequential quadratic programming (SQP) technique and stochastic based genetic algorithm (GA) to accurately obtain the global optimum solution. The performance of the optimal MRE-ATVAs with three potential designs are finally compared

Vibration Analysis of MR Fluid Sandwich Plates and Identification of Optimal MR Fluids Treatments

The MR fluids can change their rheological behavior rapidly and reversibly under an applied magnetic field. Due to their unique characteristics, these promising controllable fluids can be effectively utilized in devices and structures in a reliable and fail-safe manner to suppress vibration with minimal power requirement. While modeling of MR dampers and their integration in systems and structures to control vibration have been widely studied, there are relatively few studies on MR based sandwich structures. MR sandwich structures can provide better vibration control capability as their damping and stiffness characteristics can be simultaneously varied. Considering this, the main objectives of this dissertation are to develop accurate models to predict the vibration characteristics of MR based sandwich plates under varying magnetic field and also develop design optimization strategies to identify optimal MR fluids treatments. MR fluids typically experience low shear strain in sandwich structures and thus they operate in pre-yield region and behave like visco-elastic materials. In this study, first MR fluids have been accurately characterized in pre-yield region. Particularly new frequency-magnetic flux dependent constitute models for both loss and storage moduli have been proposed. To accomplish this, an experiment is conducted on a sandwich beam structure with aluminum face layer and MR fluid as the core layer, under different magnetic field densities. The frequency response characteristics of the sandwich cantilevered beam are subsequently measured under harmonic base excitations. Dynamic responses of the structure are also obtained using the developed finite element (FE) model. The frequency and field dependent complex shear moduli of the MR fluids (MRF 132DG and MRF 122EG) are then identified by minimizing the error between natural frequency and damping parameters obtained by experiment and FE model. The validity of the proposed constitute models is demonstrated by comparing the FE model results with the experimental data for a copper sandwich structure comprising the two MR fluids. Next, the characterized MR fluids have been used as the core layer in the fully and partially treated sandwich plates. The goal is to predict the dynamic responses of the MR sandwich plates under different levels of magnetic field. To accomplish this, finite element and Ritz models based on the classical plate theory are formulated to obtain governing equations of motion of the multi-layer rectangular and circular sandwich plates fully and partially treated with MR fluids as the core layer under different boundary conditions. Extensive experimental studies have been conducted to validate the developed models. Then, the validated models have been effectively utilized to conduct comprehensive investigation on the effect of MR fluid properties, geometry of the face layers, thickness of the core layers and magnetic flux density on vibration suppression capability of the sandwich plate structures. Finally, an optimization problem is formulated based on genetic algorithm (GA) to identify optimal locations for the MR fluid treatments, resulting in maximum variations in the stiffness and damping of the structure, corresponding to the lower three modes of flexural vibration in response to the applied magnetic field. The effects of shear deformation on the vibration properties of fully and partially treated sandwich structures are discussed, comprehensively

Mechanical characterization, constitutive modeling and applications of ultra-soft magnetorheological elastomers

Mención Internacional en el título de doctorSmart materials are bringing sweeping changes in the way humans interact with engineering devices. A myriad of state-of-the-art applications are based on novel ways to actuate on structures that respond under different types of stimuli. Among them, materials that respond to magnetic fields allow to remotely modify their mechanical properties and macroscopic shape. Ultra-soft magnetorheological elastomers (MREs) are composed of a highly stretchable soft elastomeric matrix in the order of 1 kPa and magnetic particles embedded in it. This combination allows large deformations with small external actuations. The type of the magnetic particles plays a crucial role as it defines the reversibility or remanence of the material magnetization. According to the fillers used, MREs are referred to as soft-magnetic magnetorheological elastomers (sMREs) and hard-magnetic magnetorheological elastomers (hMREs). sMREs exhibit strong changes in their mechanical properties when an external magnetic field is applied, whereas hMREs allow sustained magnetic effects along time and complex shape-morphing capabilities. In this regard, end-of-pipe applications of MREs in the literature are based on two major characteristics: the modification of their mechanical properties and macrostructural shape changes. For instance, smart actuators, sensors and soft robots for bioengineering applications are remotely actuated to perform functional deformations and autonomous locomotion. In addition, hMREs have been used for industrial applications, such as damping systems and electrical machines. From the analysis of the current state of the art, we identified some impediments to advance in certain research fields that may be overcome with new solutions based on ultrasoft MREs. On the mechanobiology area, we found no available experimental methodologies to transmit complex and dynamic heterogeneous strain patterns to biological systems in a reversible manner. To remedy this shortcoming, this doctoral research proposes a new mechanobiology experimental setup based on responsive ultra-soft MRE biological substrates. Such an endeavor requires deeper insights into the magneto-viscoelastic and microstructural mechanisms of ultra-soft MREs. In addition, there is still a lack of guidance for the selection of the magnetic fillers to be used for MREs and the final properties provided to the structure. Eventually, the great advances on both sMREs and hMREs to date pose a timely question on whether the combination of both types of particles in a hybrid MRE may optimize the multifunctional response of these active structures. To overcome these roadblocks, this thesis provides an extensive and comprehensive experimental characterization of ultra-soft sMREs, hMREs and hybrid MREs. The experimental methodology uncovers magneto-mechanical rate dependences under numerous loading and manufacturing conditions. Then, a set of modeling frameworks allows to delve into such mechanisms and develop three ground-breaking applications. Therefore, the thesis has lead to three main contributions. First and motivated on mechanobiology research, a computational framework guides a sMRE substrate to transmit complex strain patterns in vitro to biological systems. Second, we demonstrate the ability of remanent magnetic fields in hMREs to arrest cracks propagations and improve fracture toughness. Finally, the combination of soft- and hard-magnetic particles is proved to enhance the magnetorheological and magnetostrictive effects, providing promising results for soft robotics.Los materiales inteligentes están generando cambios radicales en la forma que los humanos interactúan con dispositivos ingenieriles. Distintas aplicaciones punteras se basan en formas novedosas de actuar sobre materiales que responden a diferentes estímulos. Entre ellos, las estructuras que responden a campos magnéticos permiten la modificación de manera remota tanto de sus propiedades mecánicas como de su forma. Los elastómeros magnetorreológicos (MREs) ultra blandos están compuestos por una matriz elastomérica con gran ductilidad y una rigidez en torno a 1 kPa, reforzada con partículas magnéticas. Esta combinación permite inducir grandes deformaciones en el material mediante la aplicación de campos magnéticos pequeños. La naturaleza de las partículas magnéticas define la reversibilidad o remanencia de la magnetización del material compuesto. De esta manera, según el tipo de partículas que contengan, los MREs pueden presentar magnetización débil (sMRE) o magnetización fuerte (hMRE). Los sMREs experimentan grandes cambios en sus propiedades mecánicas al aplicar un campo magnético externo, mientras que los hMREs permiten efectos magneto-mecánicos sostenidos a lo largo del tiempo, así como programar cambios de forma complejos. En este sentido, las aplicaciones de los MREs se basan en dos características principales: la modificación de sus propiedades mecánicas y los cambios de forma macroestructurales. Por ejemplo, los campos magnéticos pueden emplearse para inducir deformaciones funcionales en actuadores y sensores inteligentes, o en robótica blanda para bioingeniería. Los hMREs también se han aplicado en el ámbito industrial en sistemas de amortiguación y máquinas eléctricas. A partir del análisis del estado del arte, se identifican algunas limitaciones que impiden el avance en ciertos campos de investigación y que podrían resolverse con nuevas soluciones basadas en MREs ultra blandos. En el área de la mecanobiología, no existen metodologías experimentales para transmitir patrones de deformación complejos y dinámicos a sistemas biológicos de manera reversible. En esta investigación doctoral se propone una configuración experimental novedosa basada en sustratos biológicos fabricados con MREs ultra blandos. Dicha solución requiere la identificación de los mecanismos magneto-viscoelásticos y microestructurales de estos materiales, según el tipo de partículas magnéticas, y las consiguientes propiedades macroscópicas del material. Además, investigaciones recientes en sMREs y hMREs plantean la pregunta sobre si la combinación de distintos tipos de partículas magnéticas en un MRE híbrido puede optimizar su respuesta multifuncional. Para superar estos obstáculos, la presente tesis proporciona una caracterización experimental completa de sMREs, hMREs y MREs híbridos ultra blandos. Estos resultados muestran las dependencias del comportamiento multifuncional del material con la velocidad de aplicación de cargas magneto-mecánicas. El desarrollo de un conjunto de modelos teórico-computacionales permite profundizar en dichos mecanismos y desarrollar aplicaciones innovadoras. De este modo, la tesis doctoral ha dado lugar a tres bloques de aportaciones principales. En primer lugar, este trabajo proporciona un marco computacional para guiar el diseño de sustratos basados en sMREs para transmitir patrones de deformación complejos in vitro a sistemas biológicos. En segundo lugar, se demuestra la capacidad de los campos magnéticos remanentes en los hMRE para detener la propagación de grietas y mejorar la tenacidad a la fractura. Finalmente, se establece que la combinación de partículas magnéticas de magnetización débil y fuerte mejora el efecto magnetorreológico y magnetoestrictivo, abriendo nuevas posibilidades para el diseño de robots blandos.I want to acknowledge the support from the Ministerio de Ciencia, Innovación y Universidades, Spain (FPU19/03874), and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 947723, project: 4D-BIOMAP).Programa de Doctorado en Ingeniería Mecánica y de Organización Industrial por la Universidad Carlos III de MadridPresidente: Ramón Eulalio Zaera Polo.- Secretario: Abdón Pena Francesch.- Vocal: Laura de Lorenzi

Dynamic analysis of magnetorheological elastomer configured sandwich structures

The work presented in this thesis is concerned with the investigation of the dynamic behaviour of magnetorheological elastomers (MREs) and smart sandwich structures. An extensive review, covering existing smart materials and their applications, has highlighted that smart materials and structures can be applied to large scale structures. Comprehensive experimental tests have been carried out in order to gain knowledge and data on the dynamic shear properties and behaviour of stiffness change of MRE and MRE cored adaptive sandwich beam structures depending on magnetic fields. Dynamic shear property tests with different curing stages have been enhanced to obtain various properties. The new developed forced vibration test rig enabled forced vibration tests of MRE embedded sandwich beam with various aspects such as different magnetic field strength, various oscillations of force amplitudes, boundary conditions and damping effects under localised magnetic fields to be made. In parallel to these experimental investigations, a new theoretical model was developed by combining the magnetisation effects on iron particles in terms of the curing times. In addition, a new macro scale modelling approach for rubber like materials (nonlinear behaving materials) was made by adopting FEA analysis to obtain the optimum volume of pores and size of iron particles to enhance the performance of MREs. A higher order sandwich beam theory is extended to include damping properties of MRE. It has been demonstrated that a higher order sandwich beam theory appears to be the most versatile and accurate modelling method for a sandwich beam with an MRE core material. The results from higher order theory have been combined with a power flow analysis for the smart floating sandwich raft vibration isolation system. Finally, an experimental study was performed to illustrate the control capabilities of MRE adaptive vibration absorber for a propeller shaft in real time. From this research work, a better understanding of the dynamic behaviour of MRE embedded sandwich beam has been acquired

A study of a piezoelectric energy harvesting system using magnetorheological fluids

This thesis reports the study of a piezoelectric energy harvesting system using a thin layer of magnetorheological fluid as a soft impact mechanism to enhance the frequency of the energy generator. Currently, the major bottleneck of vibration energy harvesting is the dynamic nature of vibrations in the environment which necessitates that vibration energy harvesters change their frequency to match that of the source. This work used the variable rheological properties of magnetorheological fluids to tune the frequency of a piezoelectric energy harvester. The study employed both numerical and experimental studies to investigate the effect of using the fluid in vibration energy harvesting. The results obtained show an increase in the output voltage and frequency of the device by 9.7% and 36%, respectively. For the first time, a soft impact frequency-increased piezoelectric energy harvesting system using magnetorheological fluid is studied in this thesis

Fabrication, Characterization and Modeling of Magnetorheological Elastomers

Magnetorheological elastomers (MREs) are a novel class of magneto-active materials comprised of an elastomeric matrix impregnated by micron-sized ferromagnetic particles, which exhibit adjustable mechanical properties such as stiffness and damping coefficient in a reversible manner under the application of an external magnetic field. MREs are solid state of magnetorheological (MR) materials. In contrast to MR fluids, which provide field-dependent apparent viscosity, MREs, being a smart viscoelastic material, are capable of providing controlled field dependent moduli. Yet having a solid grasp of highly complex behavior of this active composite is a fundamental necessity to design any adaptive structure based on the MRE. This study is concerned with investigation of the static and dynamic behavior of the magnetorheological elastomers. To this end, six different types of MREs with varying contents of the rubber matrix as well as ferromagnetic particles are fabricated and characterized statically in the shear mode as a function of the magnetic field intensity. The MRE containing the highest percentage of iron particles (40% volume fraction) exhibited a notable relative MR effect of 555% with 181.54 KPa increase in the MRE shear modulus. This particular MRE was then chosen for subsequent dynamic characterization. The dynamic responses of magnetorheological elastomers revealed strong dependence on the strain and strain rate as well as the applied magnetic field intensity. Dynamic characterization is performed in shear mode under harmonic excitations under the broad ranges of shear strain amplitude (2.5-20%), frequency (0.1-50 Hz) and magnetic field intensity (0-450 mT). The strain softening, strain stiffening, strain rate stiffening and the magnetic field stiffening phenomena are identified as the nonlinear properties of MRE stress-strain hysteresis loops. Subsequently, an operator-based Prandtl-Ishlinskii (PI) phenomenological model is developed to predict the nonlinear hysteresis behavior of the MREs as functions of strain, strain rate and field intensity. The stop-operator-based classical PI model using only 10 hysteresis operators provided very accurate predictions, and it involved identification of only four parameters, which were dependent on the loading conditions. The validity of the developed Classical Prandtl-Ishlinskii model is assessed using the laboratory-measured data for MRE over a wide range of inputs. The proposed model is further generalized to predict the dynamic behavior of MRE independent of the loading conditions, which could be beneficial for controlling the MRE-based adaptive devices in real time. The results demonstrated that the proposed generalized model could accurately characterize the nonlinear hysteresis properties of MRE under a wide range of loading conditions and applied magnetic fields